The present invention relates to a sealing assembly for an ink chamber associated with an anilox roll and chamber blade assembly, and more particularly, is directed to an improved doctor/containment blade with an improved blade/seal area between the doctor blade and containment blade and the chamber seal.
Conventionally, in printing machines, such as flexographic printing machines, an ink transfer or anilox roll transfers ink to an adjacent plate roll for printing. Ink is supplied to the anilox roll from an ink chamber defined by a chamber housing which partially surrounds the anilox roll. Specifically, ink is supplied through an ink supply tube and then through an ink supply line in the chamber housing, into the ink chamber. In like manner, ink is removed from the ink chamber through an ink return line in the chamber housing and then through an ink return tube.
In order to prevent the escape of ink from the chamber, while ensuring that the ink enters the cells in the anilox roll and has a predetermined volume on the anilox roll, doctor and containment blades are provided at the exit and entry positions of the anilox roll relative to the ink chamber. The blades are fixed to the chamber housing so that the blades overhang the chamber housing and contact the anilox roll.
With this arrangement, the outer surface of the anilox roll passes through the ink chamber and picks up ink for printing. The ink is metered by means of the doctor blade held to the outlet end of the chamber housing, and sealed with a containment blade held to the inlet end, with the free ends of the blades being in contact with the outer surface of the anilox roll.
A seal is provided at each end of the blade, that is, at each end of an anilox roll for sealing the ends thereof. Examples of such arrangements are shown in U.S. Pat. Nos. 6,739,248; 6,672,207; 6,598,525; 5,983,797; 5,735,210; 5,662,042; and 5,150,651.
Examples of doctor blades used in such arrangement are shown in U.S. Pat. Nos. 5,638,751 and 6,546,861.
Each seal is formed by a compressible or deformable body. Since the seals provided at each end of the anilox roll function to seal the ends of the ink chamber, each seal must lie against the peripheral surface of the rotating anilox roller. As a result, each seal is therefore exposed to mechanical stresses as well as wear. Further, during the printing operation, the blades, which press against the anilox roll, also wear. The geometry of the sealing function between the anilox roll, the two blades and the end seal changes.
Conventionally, each end of a blade sits upon a flat supporting area of the respective seal. As a result, a gap may be created at the opposite ends of the blades where they are held by the chamber seals. However, there is uneven wear on the ends of the blades adjacent the seals, which tends to cause leakage of ink at the ends of the anilox roll. As the doctor blades are forced against the anilox roll and, in particular, when the doctor blades wear unevenly in the sealing area, the sealing and doctor blades may flex or bow outwardly relative to the flat supporting area of the seal, due in part to the flimsiness of the thin blades, pressure on the blades, dried ink under the blades, fluid pressure in the chamber, etc. Thus, the areas where the anilox roll, blades and seals join are susceptible to leakage because of geometric changes.
The above U.S. patent application Ser. No. 12/710,763 provides a solution to the above problems by providing an improved doctor blade and containment blade with additional wear resistance, improved leakage resistance, increased rigidity and increased wear life at the position of the end seals. This is accomplished by a wear element which increases the stiffness and/or wear of the thin plate of the blades, the wear element mounted to a surface of the thin plate at least at a position corresponding to the end seals, such that the thickness of the reinforced blade is greater at the opposite ends thereof which lie against the seals than at positions thereof between the end seals.
However, the wear element increases the thickness of the blade thereat. Because of the extra thickness thereat, when the wear element hits the anilox roll, there is increased force by the anilox roll on the blade at this position, which can result in undesirable effects. Specifically, because of this increased force on the blade, the blade wears faster thereat, even though the life of the blade at this position is still longer than a blade without the wear element. There are also wiping problems thereat which can cause dripping of the ink.